Kotaru is 5 Months Old Today!

Today, our second little boy turned 5 months old! The sands of time continue to slip through our fingers and no matter how hard we grasp at those grains, it seems that there is nothing we can do to slow the growth of our boys.
At a birthday party yesterday, we met a 6 month old that is definitely at least 50% bigger in height and weight than Ko. We always knew that Ko is a slim little guy, but the size of that giant half-year old made us think about Rai at this age, too. At 5 or 6 months, Rai was also bigger and stronger than Ko. Kotaru seems a lot more like a little infant than Rai did at this same age. Why?
Formula. Formula is the answer. From birth, Rai was drinking formula and, by 3 months, it was all he was eating. He would chug bottle after bottle of that stuff. Ko, on the other hand, continues to drink only breast milk and it's hard to imagine that he drinks 8-12 ounces of it per feeding. So, guess what that giant 6-month old is eating. Yes, it's formula. I'm surprised they don't sell that stuff at GNC stores.